Function Notation - Definition & Examples

In Lillie's fridge, there are apples, pears, mandarins, bananas and persimmons. There are $x$ apples and $y$ persimmons. There are twice as many pears as apples; there are twice as many mandarins as pears. There are 3 less bananas than persimmons. In total, there are 16 items of fruit in the fridge.